diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
new file mode 100644
index 0000000..2cdccbd
--- /dev/null
+++ b/CONTRIBUTING.md
@@ -0,0 +1,136 @@
+This is a general guide if you want to report bugs, ask questions,
+request features or submitting patches.
+Please take a moment to review this document in order to make the
+process easy and effective for everyone involved.
+
+This document is adapted from [necolas/issue-guidelines](https://github.com/necolas/issue-guidelines)
+
+## Table of Contents
+- [Channels](#channels)
+ - [The Issue Tracker](#issue-tracker)
+ - [The Mailing List](#mailing-list)
+ - [Contacting the Author](#author)
+- [Guidance](#guide)
+ - [Ask Questions](#ask-question)
+ - [Bug Reports](#bug-report)
+ - [Feature Requests](#feature-request)
+ - [Pull Requests](#pull-request)
+
+***
+
+## Channels
+
+A few channels are available to reach the developers, please find the most proper one for your purpose.
+
+
+### The Issue Tracker
+
+The [Issue Tracker](https://github.com/coolwanglu/pdf2htmlEX/issues)
+is the best way for
+[bug reports](#bug-report),
+[features requests](#feature-request)
+and [submitting pull requests](#pull-request).
+
+Please respect the following restrictions:
+* Do not post personal support requests, (e.g How can I call pdf2htmlEX in Java?). Use the mailing list, or [Stack Overflow](http://stackoverflow.com) instead.
+* Keep the discussion on topic and respect the opinions of others.
+* Posts violating the above restrictions may be removed without any notification.
+
+
+### The Mailing List
+
+The [Mailing list](pdf2htmlex@googlegroups.com) is set up for discussion and announcements.
+You are welcome to [ask any question](#ask-question) about pdf2htmlEX there.
+However do not report issues or submit patches there, since it's terrible to keep track of them.
+
+
+### Contacting the author
+
+pdf2htmlEX is mostly written and maintained by Lu Wang (王璐).
+His email and twitter address of the author can be found in
+[README.md](https://github.com/coolwanglu/pdf2htmlEX/blob/master/README.md).
+
+Please post only messages that do not fit into the above channels, for example:
+- Private messages to the author.
+- Sample files with private information. (But please still report the bug via the issue tracker)
+
+Please expect a _long_ delay，since the messages are usually archived and checked on a regular basis.
+
+
+## Guidance
+
+Here are a few tips for different types of messages.
+Lots of your time may be saved if you follow the guidelines.
+
+
+### Ask questions
+
+If you need any help or have issues using pdf2htmlEX,
+follow the following steps to get it resolved as fast as possible:
+
+First of all, did you realize that your question might have been already answered in one of the following places?
+
+- [pdf2htmlEX Wiki](https://github.com/coolwanglu/pdf2htmlEX/wiki)
+- The manpage (run `man pdf2htmlEX`)
+- Old posts in the [mailing list](#mailing-list) or the [issue tracker](#issue-tracker)
+- [Google](http://www.google.com/)
+
+If you cannot find anything useful there, do not hesitate to post in the [mailing list](#mailing-list).
+On the other hand, if you think it's something wrong about pdf2htmlEX, please [report a bug](#bug-report) instead.
+
+
+### Bug Reports
+A bug is a demonstrable problem that is caused by the code in the repository.
+A perfect bug report may help the developer to identify the cause and locate the problematic code quickly.
+
+Before you report any bug:
+- Use the latest git version of pdf2htmlEX, since the issue may have been already fixed.
+- Search for previous issues (open or closed), to make sure that the issue has not been reported before.
+
+A good bug report shouldn't leave others needing to chase you up for more information.
+The developers may be very familiar with the code base of pdf2htmlEX,
+but they may not know anything about your environment or what steps you have done,
+unless you have them stated.
+Please try to be as detailed as possible in your report.
+Good examples include: [#58](https://github.com/coolwanglu/pdf2htmlEX/issues/58), [#183](https://github.com/coolwanglu/pdf2htmlEX/issues/183) and [#226](https://github.com/coolwanglu/pdf2htmlEX/issues/226).
+
+If you are not sure, please try to answer the following questions:
+
+- What's your operating system?
+- What's the version of pdf2htmlEX and depended libraries? (You can post the output of `pdf2htmlEX -v`)
+- Which browser(s) are you using?
+- What steps will reproduce the issue? — please try to remove unnecessary steps
+- What's the result and what did you expect? — e.g. you can post screenshots
+- What error messages did you see?
+- Where's the affected PDF file? — e.g. you may upload the file via Dropbox and post a link here
+
+Especially for issues regarding building pdf2htmlEX:
+- Which compiler are you using?
+- What's the output of `cmake` and `make`?
+- What's the content of `CMakeList.txt`?
+
+
+### Feature requests
+
+Feature requests are welcome. But take a moment to find out whether your idea
+fits with the scope and aims of the project. It's up to *you* to make a strong
+case to convince the project's developers of the merits of this feature. Please
+provide as much detail and context as possible.
+
+
+### Pull requests
+
+Good pull requests - patches, improvements, new features - are a fantastic
+help. They should remain focused in scope and avoid containing unrelated
+commits.
+
+**Please ask first** before embarking on any significant pull request (e.g.
+implementing features, refactoring code, porting to a different language),
+otherwise you risk spending a lot of time working on something that the
+project's developers might not want to merge into the project.
+
+Please read [_Using Pull Requests_](https://help.github.com/articles/using-pull-requests/)
+if you are new to pull requests.
+
+**IMPORTANT**: By submitting a patch, you agree to allow the project owner to
+license your work under the same license as that used by the project.
diff --git a/share/pdf2htmlEX.js.in b/share/pdf2htmlEX.js.in
index 7af26ce..7edf198 100644
--- a/share/pdf2htmlEX.js.in
+++ b/share/pdf2htmlEX.js.in
@@ -663,13 +663,12 @@ Viewer.prototype = {
/**
* @param{number} ratio
* @param{boolean} is_relative
- * @param{number=} offsetX
- * @param{number=} offsetY
+ * @param{Array.=} preserve_pos preserve the position after rescaling
*
* TODO: offsetX/Y is by default the center of container
* TODO consider scale on offsetX/Y
*/
- rescale : function (ratio, is_relative, offsetX, offsetY) {
+ rescale : function (ratio, is_relative, preserve_pos) {
var old_scale = this.scale;
var new_scale = old_scale;
// set new scale
@@ -683,14 +682,11 @@ Viewer.prototype = {
this.scale = new_scale;
- if (! offsetX)
- offsetX = 0;
- if (! offsetY)
- offsetY = 0;
+ if(!preserve_pos)
+ preserve_pos = [0,0]
// Save offset of the active page
var active_page = this.pages[this.cur_page_idx];
- if (!active_page) return;
var active_page_ele = active_page.page;
var prev_offset = [ active_page_ele.offsetLeft, active_page_ele.offsetTop ];
@@ -703,14 +699,13 @@ Viewer.prototype = {
var container = this.container;
// Correct container scroll to keep view aligned while zooming
var correction_top = active_page_ele.offsetTop - prev_offset[1];
- container.scrollTop += correction_top + offsetY;
-
+ container.scrollTop += correction_top + preserve_pos[1];
// Take the center of the view as a reference
var prev_center_x = container.clientWidth / 2 - prev_offset[0];
// Calculate the difference respect the center of the view after the zooming
var correction_left = prev_center_x * (new_scale/old_scale - 1) + active_page_ele.offsetLeft - prev_offset[0];
// Scroll the container accordingly to keep alignment to the initial reference
- container.scrollLeft += correction_left + offsetX;
+ container.scrollLeft += correction_left + preserve_pos[0];
// some pages' visibility may be toggled, wait for next render()
// renew old schedules since rescale() may be called frequently